1. Field of the Invention
The invention relates to a method and device for regulating/controlling the output moisture content of tobacco conditioned by a loosening/conditioning and optionally casing (saucing) drum.
2. Description of the Related Art
It is in the tobacco industry, especially in the cigarette industry, that a loosening/conditioning and optionally loosening/conditioning/casing (saucing) drum has the function of loosening the raw tobacco furnished in bales, casing it (also called saucing so that hereinafter casing (saucing) is used) and conditioning it for further steps in the process of preparing the tobacco. Special embodiments of such drums are known, for example, from WO 90/13231, EP-B-0 424 501 and EP-A-0471 513.
In such a drum, water and/or steam is injected into the tobacco mass contained in the drum, which is supplied to the drum in the form of bales or bale pieces.
A typical embodiment is evident from FIG. 5 of EP-A-0 471 513 wherein the water nozzles are located in the infeed region of the drum and are configured as duplex nozzles introducing a mixture of water and steam. The intention is that the tobacco leaving the drum has an output moisture content of approx. 12% to approx. 16.5%, the precise value depending on the subsequent steps in the method of preparing the tobacco.
Experience has shown that the optimum target value necessary in each case fails to be attained by these known methods, thus resulting in fluctuations in the output moisture content of the tobacco and corresponding problems in subsequent steps in the method of preparing the tobacco.
The invention is thus based on the object of providing a method and device in which the aforementioned disadvantages do not occur and in which, more particularly, the output moisture content of the tobacco may be regulated/controlled to an optimum value.
This object is achieved in accordance with the invention by a method for regulating the output moisture content of tobacco conditioned by a loosening/conditioning and optionally a casing (saucing) drum 28, comprising injecting into the infeed region of the drum through a first nozzle a throughflow of water regulated depending on the target value for the output moisture content of the tobacco and the actual set values for the tobacco mass flow, the steam throughflow and the input moisture content of the tobacco; and injecting into the outlet region of the drum through a second nozzle a throughflow of water, the target value of which is computed depending on the target value and actual value for the output moisture content of the tobacco; and wherein the discharge hood of said drum is heated by a steam heat exchanger.
Expedient embodiments read from the corresponding sub-claims.
The advantages achieved by the invention are rooted in employing a two-stage infeed of water, namely, for one thing, in the infeed region of the drum and, for another, in the outlet region. The target value for the throughflow of water in the infeed region of the drum is calculated, i.e. dependent on the target value for the output moisture content of the tobacco which in turn depends on the subsequent steps in the method, and on the actual values of the tobacco mass flow, input moisture content of the tobacco and steam throughflow applied to the drum.
In the infeed region of the drum a throughflow of water is thus employed tailored to the method which, however, is yet to be rendered strictly conform with the target value for the output moisture content of the tobacco, this later being exactly set by means of a second water infeed into the outlet region of the drum by calculating the target value of this second water infeed from the target value and actual value for the output moisture content of the tobacco. It is not until the second stage that finalizing the regulation of the output moisture content of the tobacco is fine xe2x80x9ctunedxe2x80x9d so that a value is attained with high accuracy which is optimum for subsequent steps in the method of preparing the tobacco.
In one preferred embodiment the throughflow of water for water supply in the outlet region of the drum is fine tuned by comparing it to the actual value of the injected flow of water to assure minimum departures from the target value for the output moisture content of the tobacco.
Since the casing (sauce) likewise supplied to the drum contains water, i.e. up to 90% in extreme cases, the target value for the throughflow of the casing (sauce) applied to the drum is taken into account in a preferred embodiment when calculating the throughflow of water for the infeed region of the drum so as avoid heavy departures or fluctuations in this respect, too.
As it reads, calculating the throughflow of water for the infeed region of the drum is done by a formula which takes into account the salient influencing parameters, namely the target value for the output moisture content of the tobacco, the actual value for tobacco mass flow, the actual value for the input moisture content of the tobacco, the actual value for the steam throughflow and in conclusion, where needed, also the target value for the casing (sauce) throughflow.
It has been discovered to be important that the tobacco mass flow supplied to the drum should be maintained constant to assure in this respect consistent and homogenous conditions in the method. It is for this reason that the tobacco mass flow supplied to the drum is regulated by means of a weighing belt disposed between the drum and a slicer upstream of the drum, this slicer being used to apportion the tobacco in slices, whereby the cutting frequency of the slicer is dictated by the weighing belt so that a constant tobacco mass flow is supplied to the drum with high consistency.
In accordance with one advantageous aspect there is provided between the slicer and the weighing belt a first photoelectric barrier located at the start of the impact belt and activating the slicer when receiving a xe2x80x9cno slicexe2x80x9d alert. To ensure a continuous supply of tobacco bale portions to the weighing belt any gaps in supply are xe2x80x9cseenxe2x80x9d by a second photoelectric barrier at the end of the impact belt when a xe2x80x9cno slicexe2x80x9d alert is received, these gaps being closed by elevating the speed of the impact belt to thus also contribute towards a constant tobacco mass flow.
In accordance with one preferred embodiment the two nozzles are configured as duplex nozzles injecting a duplex mixture of water and steam. Both the steam A flow supplied and the water flow supplied are detected and tuned to the corresponding target values so that here too heavy fluctuations are practically eliminated.
The casing (sauce) infeed too is engineered by means of a duplex casing/steam nozzle arranged in the outlet region of the drum.
For regulating the temperature of the drum, steam is fed into a recirculating air passage of the drum, this steam flow too being regulated/controlled and taken into account in regulating/controlling the output moisture content of the tobacco.
It has been discovered to be expedient when the discharge hood of the drum is indirectly heated by steam heat exchangers so that in this respect no deposits and more particularly no condensation can materialize, thus ensuring consistent conditions in the method. The door of the discharge hood is electrically heated to avoid condensation and deposits.
In accordance with another preferred embodiment the drum is provided with an xe2x80x9cpneumatic bladexe2x80x9d which scrapes soilage from the surface of the drum which could otherwise result in random conditions in the method and more particularly in heavy fluctuations in heat transfer.